Aluminum alloys find a wide variety of applications due to their favorable combination of mechanical properties, including strength-to-weight ratio, low temperature (cryogenic) properties, corrosion resistance and notch toughness. The challenge with aluminum alloys is to maintain these mechanical properties and corrosion resistance at weld joints and weld heat-affected-zones.
Heat-treated aluminum alloys tend to substantially soften during most known welding processes, resulting in weaknesses at and around the weld joint. Furthermore, some welding processes, such as resistance spot welding (“RSW”), significantly reduce thickness in the workpiece at the weld joint, which further erodes the strength and other mechanical properties at and around the weld joint.
In addition to the obstacles presented by degradation of mechanical properties resulting from conventional welding processes, certain high strength aluminum alloys are not easily weldable. Specifically, high strength aluminum alloys tend to present cracks during solidification after the welding heat has been terminated. Unfortunately, it is typically the high strength aluminum alloys that are not easily weldable.
Relatively new weld processes, such as friction stir welding, have improved the mechanical properties of aluminum alloys at and around weld joints. However, the equipment and tooling associated with friction stir welding are very expensive and difficult to maintain. Furthermore, friction stir welding often results in cross-section reductions at the weld joints, which are left behind by tooling being withdrawn from the welded part. Therefore, even new welding processes, such as friction stir welding, result in some loss of mechanical properties (e.g., strength) at and around weld joints.
Accordingly, those skilled in the art continue to seek new welding techniques, including welding techniques that do not degrade the mechanical properties or corrosion resistance of the workpiece at and around the weld joint.